With EACH OTHER!!!
It is the sweetest thing you've ever seen. Jonathan giggles at Thomas and Thomas grins back. Today Thomas said "ahn-goo" to Jonathan, and Jonathan thought it was hilarious and walked around copying him. Jonathan keeps Thomas well-supplied with puzzle pieces and small cars and trucks, and Thomas rewards him with smiles and coos, which Jonathan thinks are pretty neat!
I tried to get some video, but of course as soon as I brought the camera out, all sweetness came to an end. ;) Oh well.